1. Field of the Invention
The invention relates to a rotatable device having an aerostatic bearing and also a direct drive in the form of a segmented ring motor. Devices of this kind are preferably used as rotors in computer tomographs (CT scanners).
2. Description of the Relevant Art
In computer tomographs an X-ray tube rotates together with a detector disposed opposite to it around the body of a patient. The X-ray tube and the detector are mounted to the rotating part of a gantry, with the rotating part being supported to be rotatable relative to a stationary part. In modern computer tomographs of high resolution, the rotating part of the gantry rotates at high rotation numbers, for example 300 r.p.m. Simultaneously a very high positional tolerance of the gantry in ranges distinctly below 1 mm is required. With this, mechanical bearings frequently approach limits of what is technologically possible. Here, an elegant way of providing a bearing function is by means of an aerodynamic bearing, also known as an air bearing.
U.S. Pat. No. 6,404,845 B1 discloses a gantry of a computer tomograph having an aerodynamic bearing. In this, a rotating part of the gantry is held in a desired position by axially and radially disposed bearings. Here it is difficult to control the function of an axial bearing. This consists of two bearings disposed opposite to each other on opposite sides of the rotating body of the gantry. A problem with this is that smallest of changes of the configuration of the rotating body, in particular of a distance between the locations of support of the oppositely disposed axial air bearings directly affect the bearing clearance and therewith the bearing properties.
A further improvement of this arrangement is disclosed in WO 2008/017498 A2. This document describes a bearing arrangement in which at least one of the axial bearings can be moved along an axial direction towards its bearing basis, in order to compensate these fluctuations of thickness of the rotating body.